While numerous advancements have been made in the emulsions field, there are several long standing needs that remain. For example, as the percent solids of an emulsion increases, in most emulsions the viscosity also increases. Emulsions having a solids level greater than 75 weight % can become so viscous that they are non-pourable. This effectively renders such emulsion products unusable in many applications due to the handling difficulties of such viscous compositions.
Another long standing need in this field is to stabilize emulsions with a minimal amount of surfactants. This is a particular need when the emulsions are used to form coatings, such as protective architectural coatings. Residual surfactant on coatings formed from emulsions can have several detrimental effects on the physical property profile of the coatings such as decreased hydrophobicity and/or poorer dirt resistance. The use of emulsions with minimal amount of surfactants is also highly desirable for application in personal care products, especially for skin and cosmetic formulations where residual surfactants may cause skin irritation.
Reducing the presence of solvents, un-reacted siloxanes, catalyst residues, cyclic polymerization byproducts, and other impurities in silicone emulsions is an ongoing challenge in the art. The need to reduce such impurities may arise, among other reasons, when such impurities are incompatible with downstream applications (for example, medical, cosmetic, and personal care applications), where the presence of such impurities would reduce the stability of an emulsion, or where regulatory requirements require removal or reduction of their presence. In particular, there is an interest to reduce the presence of cyclosiloxanes, such as octamethylcyclotetrasiloxanes and decamethylcyclopentasiloxanes, in silicone emulsions.
U.S. Pat. No. 4,824,877 to Glover et al teaches High Polymer Content Silicone Emulsions. More specifically, Glover teaches emulsions of polydiorganosiloxane having a high polymer content and yet a relatively low viscosity by blending 100 parts by weight of a polydiorganosiloxane macroemulsion having a high polymer content with 1 to 70 parts by weight of a polydiorganosiloxane microemulsion having a high polymer content. However, since Glover's process is based on blending a macro and microemulsion, Glover's emulsions may still contain higher concentrations of surfactants and cyclosiloxanes.
U.S. Pat. No. 4,874,547 to Narula teaches bi-modal silicone emulsions. Narula relates generally to silicone-in-water emulsions and, specifically, to a process for emulsifying a high viscosity silicone in water, using only nonionic surfactants, and to the emulsions obtained therefrom. In a particular aspect Narula relates to a process for emulsifying a bi-modal silicone fluid comprising a polydimethylsiloxane having a viscosity of at least 30,000 centipoise at 25° C. and a substantial amount of a volatile polydimethylsiloxane.
Thus, a need exists to identify a process that provides emulsion products having high solids contents that remain pourable. A further need exists to reduce the concentration of surfactants in emulsion products, especially at high solid content emulsions. Yet, a further need exists to provide silicone emulsions having reduced content of cyclosiloxane concentrations.